Spot Hero – www.spothero.com.  Offers discounted parking options at hotels in the Crystal City area.  You can use this system as a “guest” without creating an account.  In the search box asking “where are you going,”  type in “Crystal Gateway Marriott” and the search will provide options.  Interestingly, it appears there are options AT the Crystal Gateway Marriott cheaper than the discounted rate of $40 the hotel provided to our group.  No in-and-out privileges.  Free cancellation up to the time your reservation begins.  Reserve soon before prices go up or availability is gone. 

DCA Airport parking – https://www.flyreagan.com/.  DCA accepts reservations to park in their daily garages, which appears to be cheaper than at the hotel.  No in-and-out privileges.  Catch the hotel shuttle (or Honor Flight shuttle) at either Terminal 1 or 2 to get to the hotel after parking.  Parking at the airport does fill up (especially being a holiday weekend), so reservations are highly recommended if you plan to park there.  Discounted rates will go up as the date gets closer; and when the lots reach capacity, reservations will no longer be accepted.  You may cancel your reservation for any reason, at any time up to 1 hour before the start of the reservation without charge.